Depending on the work pieces that need to be joined, it is often desirable to join the flexible materials without actually stitching the materials together as this would create holes in the materials through which liquid could penetrate. For example, flexible thermoplastic materials, such as vinyl sheeting or coated fabrics would benefit from being joined together without stitching.
One common method for forming such a joint is by welding two or more flexible materials together using radio-frequency (R-F) welding which fuses the materials together to form an integral weld, thereby eliminating the need to stitch the materials together. This method is also known as high-frequency welding.
Prior art methods for forming R-F welds between flexible materials have typically included the use of bar presses, where a single, elongated electrode bar is attached to a moveable upper or lower platen of a press. The desired work pieces that need to be joined are positioned on a lower platen of the press, and once the work pieces are in position, the upper platen and attached electrode bar are lowered to compress the work pieces between the electrode bar and the bottom platen. During the compression of the work pieces, the radio-frequency energy is applied to the electrode bar to weld the work pieces together.
This typical welding system has a number of drawbacks. Depending on the positioning of the desired welds, the work piece may have to be repositioned on the lower platen, and the upper platen engaged again to continue the welding process. Therefore depending on the welds required, multiple, repeated operations are required resulting in manufacturing inefficiencies, including long cycle times in the production a welded article, and inoperative and under-utilized welders during the down time between welds. These inefficiencies and equipment underutilizations drive up manufacturing costs, making the manufacturer less competitive in the marketplace. Also most of these welding systems included a fixed R-F welding machine, and sliding work platforms which does not allow for large work pieces to be welded efficiently.
Furthermore as noted above, typical welding machines have a single electrode that is fixed to the upper platen of the welder that therefore engages the topside of the flexible work piece. This single electrode is therefore used repeatedly to either weld the same parts over and over again, or to weld repeated hits on the same part (for example, a long seam would require many repeated hits by a shorter electrode). As a result of the dedicated nature of this type of welder, the welder is not very flexible to retool when different products need to go into production. Other typical welding systems may not have the welding electrodes connected to the upper platen of the welder, but still have the welding electrodes located above the fabric work piece. Furthermore these systems typically must have the weld electrode engage the positioning features which are either fastened to an electrode base, or directly to the work platform making weld electrode changeover from one product to another very slow and inefficient.
Moreover depending on the industry, a welding system may be required to provide a large variety of R-F welded parts, but in relatively small quantities. To meet this challenge of being able to produce a large variety of welded parts in small quantities, the welding system has to be able to accommodate quick and flexible retooling specifically with respect to the electrode configuration.
Finally it is also important to control the appearance of the fabric at the weld location specifically the gloss level, and to provide an inherent method of preventing the flexible work piece from sticking to the upper platen of the welder. Traditionally mechanical clamps are used to hold the flexible work piece in place. The positioning of these clamps are however prone to human error and are labour intensive. With a typical industry that utilizes dedicated R-F welders for specific weld tasks, a system of automated clamps or other mechanical means of preventing parts from sticking to the electrode on the upper platen could be developed to overcome this issue. An automated clamping system however would not be feasible where a large variety of parts in small quantities are needed.
Thus a R-F welding system for welding flexible work pieces which allows for easy reconfiguration of multiple electrodes with maximum flexibility of electrode layouts, maximum process automation and repeatability on large R-F welders with large welding platforms, easy and accurate positioning of the work pieces on the weld platform, easy removal of the work piece once welding has occurred, and improved appearance of the final product is desirable.